Resistance device.



H. W. LEONARD.

RESISTANCE DEVICE.

APPLICATION FILED MAR.29, 1909.

Patented Dec. 6, 1910.

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H. W. LEONARD.

RESISTANCE DEVICE. APPLICATION FILED name, 190v.

Patented Dc.6,1910.

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uh/Means" HARRY WARD LEONARD, OF BRONXVILLE, NEW YORK.

RESISTANCE DEVICE.

Specification of Letters Patent.

PatentedDec. 6, 1910.

Application filed March 219, 1909. Serial No. 486,297.

To all whom it may concern:

Be it known that I, HARRY WARD LEONARD,

' a citizen of the- United States, residing at Bronxville, in the county of Westchester and State of New York, have invented certain new and useful Improvements in Resistance Devices, of which the following is a full, clear, and exact specification.

This invention relates to devices in which electric energy is intentionally converted into heat.

One of the devices to which my invent-ion is applicable is a field rheostat for a large generator. It is, however, capable of application in other relations.

Among the principal objects of my invention are reduction of first cost; reduction of vweight; reduction in the number of parts; the employment of resistive material of very low temperature coefficient, light in weight and of large surface, strong in re sisting strains of usage and non-oxidizing; simplicity, ease, cheapness and expedition in making renewals or repairs; an econom ical and efiicient arrangement of the resist ance so as to reduce the maximum temperature of many of the parts as will appear hereinafter.

In the preferable embodiment of my in ances arranged in series and I employ a plurality of such series. For example, I may, in a rheostat, arrange the resistance units in two concentric circles, the movable contact lever of the rheostat being pivoted in a central point and having a moving contact at one end making connection wit-h the outside circle of unit resistances and having a moving contact at the other end making connection with the inside circle. 'Thus the movable contact element acts as a bridge carrying the current across from one circle to the other so that the steps of one circle which are in circuit are in series with steps of the other circle of unit resistances. By

this arrangement What may be conveniently turned on, carrying current and being there fore hot while. the other port-ions of the rheostat. will not carry current and Wlll vention I employ a plurality of unit resist I therefore be comparatively cool. In a tapered current rheostat, such as a field rheostat, the heated step next to the movable element is hotter than any preceding one and hotter than it itself will be in any other position of the movable element. In such an appllcation a'large number of steps are required and the development of two hot spots as indicated gives an increased capacity for a certain size and weight because of the improved facilities for dissipating the heat generated by the passage of current through the rheostat. Preferably the moving contacts at the opposite ends of the contact lever are independently movable so as to adjust themselves tothe contacts over which they are respectively passing.

The specific design referred to gives a perfect distribution of the heat generated in the rheostat circuits secures a very compact rheostat and by using a movable contact element in the form of a double connected contact lever, the friction on the pivot is re duced becauseof the balanced pressure on the shoes at the two opposite ends of the lever. Moreover, it is unnecessary to carry current through any moving contact except the contact shoes themselves, whereas customary forms either the pivotal contact car'- ries the current or there are additional metal arcs and corresponding moving contacts, all of which are rendered unnecessary by the present construction. These advantageous features are of especial importance in connection with remote controlled rheostatsfor many reasons, one of which is that a small amount of power is required to. move the contact lever, while the moving contacts are self-adjusting and self-cleaning. v

The construction of the resistance units, considered individually, gives rise to numerousadvantages of whlchthe following may be referred to.

The cost is low because very thin ribbonlike, resistive conductor can be used, the

total weight being very small and'the cost" parts necessary. a

A much more constant resistance 1s obtained than with cast iron or other customary forms, because the temperature co- 15 loy employed, and the length of the unit, it

efficient of the resistance ribbon is very low 1 and there is a minimum length of copper or similar conductor.

Owing to the simple construction, the chances of troubles due to connections are greatly reduced while there is no possibility of short-circuits between connecting or lead wires as they are entirely eliminated.

The construction makes it readily possible to 'get an extremely Wide ran e in the ohmsand amperes of a step, and also, when needed, a suflicient range in wattage per step. By varying the width and thickness of the-ribbon used, the resistivity of the albecomes readily possible to get any variation in ohms with any desired amperes and any desired watts per ste within the desirable limits of commercia practice.

The insulation of the resistive conductor can be made extremely hi h because the metal parts are all supported by high grade insulating material, such as porcelain and it is not necessary to rely at all upon rubber, asbestos, mica, cements, or any of the many forms of commonly employed insulating materials, which are likely to depreciate in time or become affected by moisture, dust, or other insulator-affecting substances 0 or conditions. i

The ribbon form of resistive conductor lends itself readily to securing ample and reliable contact between the resistive material and the strap-like copper terminal pieces employed, without themecessity: for soldering, which is likely, in many cases, to depreciate the quality ofthe materials soldered.

It is readily possible to inspect, remove,

replace, repair, modify or adjust the unit resistances or any of their parts and, since 1 many of the parts are interchangeable and uniform independent of the ohms, amperes I or watts of the steps, only a few repair parts 4-5 are necessary to make any repairs needed. A few arts and a small inexpensive lot of sheet erman silver of several different thicknesses, make it possible for any workman in a few minutes, with ordinary tools,

3 to make repairs, or, in fact, to make new units of any desired electrical properties within very wide limits.

The chance of breakage of the resistive. material due to shocks in shipment, installation or use, is greatly reduced as compared with cast iron grids or any usual forms of resistances for relatively large currents.

The strains due to heating and cooling of the resistive material are reduced to a minimum and practically eliminated, whereas in cast iron grids or other familiar types of resistances, these strains are frequently destructive or troublesome. I

55 The risks of breakdown of insulation due 1 to lightning or high voltage discharges, are reduced to a minimum because of the permanent reliable character of the insulation and the large air spaces. A

The risks of short-circuits or leakage between the diflerent parts of the rheostat, such, for instance, as those due to oil, dust, filings, mud, ice, or condensed moisture on the surface, are reduced to a minimum.

The forni of the unit, its method of mount- .ing, and its position with relation to the face illustrate the invention,'Figure l is a side elevation of a resistance unit. Fig. 2 is also a side elevation viewed from a point ninety degrees removed from the view-point of Fig.

1. Fig. 3 is a bottom plan view of the unit. Fig. 4 is an enlarged section on line 4% of Fig. 2, looking in the direction of the arrow. Fig. 5 is a partial vertical section on the line 55 of Fig. 1, looking in the direction of the arrow. Fig. 6 is an elevation of the lower end of the unit looking in the direction of the arrow 6 in Fig. 1. Fig. 7 is a perspective view of one of the unit terminals, Fig. 8 is a perspective view of arr other of the unit terminals. Fig. 9 is a bottom plan view of the rheostat partly broken away, showing the manner of application of the resistance units thereto. Fig. 10 is a top plan View of a rheostat showing the stationary contacts and the movable contact element. Fig". 11 is a diagram of the electric connections through the rheostat. Fig. 12 is a bottom plan view of one end of the movable contact element showing the contact shoe; and Fig. 13 is a partial section on the line 13-13 of Fig. 12. Fig. 14 is an enlarged perspective view of the bottom portion of the unit.

Referring to the drawin and first to Figs.

1 to 8 inclusive and 14,eac unit comprises a support, consistingof the porcelain insulating elements at its ends-which are adjustably supported by the metal rod 1. At one end the element consists of two spools 3 and 4 through which extends a metal bolt 5, this bolt extending through an eye 6 of the metal rod 1. The porcelain insulating element at the other end-of the unit consists of a p0rcelain block 7 through which the screw threaded portion 8 of the rod 1 extends. This element is secured upon the rod 1 by means of the nut 9, ,while it is held from moving I bolts 24 and 25 do not come in contact with toward the support at the other end ot the unit by means of the nut 10. It will be apparent that the distance between the elements may be adjusted by adjusting the nuts 9 and 10 upon the rod 1 and that this ad 'justment is along the line of greatest dimension of the unit. The resistive conductor 11 of the unit is ribbon-like, flexible, reflexed (asshown best in Fig. 1) and is of non-os idizable material, such as German silver. One end of this conductor passes withina loop 12 of conducting material such as copper, and also within this loop is inserted an end of the terminal 13, also of copper and the screw 14 is passed through the loop, the terminal and the resistive conductor. (A look nut 15, bearing upon a washer 16, firmly clamps the terminal, loop and conductor together. The porcelain block 7 is provided with a recess 17 for the reception of the nut 15, washer 16. The end of the conductor, together-with the terminal 13 is secured to the block 7 by means of a nut 18 upon the screw 14, the screw passing through the block land the nut 18 being within the recess 19 upon the opposite side of the block. From the termina. l 13 the resistive conductor passes upwardly to the spool 4 and down to the opposite side of the block 7. Here the conductor is bent at right angles to extend along the block, this portion extending along the block being in dicated by the numeral 11; then it extends upwardly and over the spool 3 and downwardly again to the block 7 and terminates at the terminal 20. Preferably the conductor assumes the form of a long narrow arch as shown in Fig. 1. For convenience we will. call the side of the block 7 upon which the terminals 13 and 4 20 are located, the front side. Terminal 20 and the extremity of the resistive conductor are secured to the 2 front of the terminal block in .precisely'the same way as described in connection with the other extremity of the conductor and the terminal 13. .()n the back side of the block 7 the resistive conductor is surrounded by a loop of copper 21 and within this loop and next to the resistive conductor is entered the elongated part 22 of terminal 23.v

This part 22 of the terminal 23 is substantially of the same length as that portion of the resistive conductor where it is at right angles to its major length andthe resistive conductor and terminal 23 vare clamped together by bolt-s 24 and 25 which pass through the loop 21, the resistive conductor,

and thepart 22 of the terminal 23. The terminal 23 is held in position by the nut 9 and the rod 1 which extends-through it.

The head of the bolt 25 extends into the, recess 26 and correspondingly the head of the bolt 24 extends into the recess 19. The re cessesl!) and 26 are deep enough so that the the terminal 23 is not in the same plane with the terminals 13 or 20. In this'way contact of the,terminals-is avoided with economy of lateral space. The block 7 is pro vided with a rib 29'between the terminals 20 and 13, thereby insuring good insulation between them and preventing accidental contact between them both by preventing the terminals from being accidentally pushed together and also by increasing the surface over which contact might be formed by dust, oil, or the like. The parts having been assembled as described, it will be apparent that the resistive conductor may be stretched between the resistance elements at the ends of the unit by adjusting nuts 9 and 10 and that the conductor being placed under tension any slack which might otherwise be occasioned by heating of the conductor will be taken up. so that the conductor will be maintained in proper position, regardless of its temperature. The terminals 13, 20 and 23 are made of stiff copper sheet, so that they are adapted to support the unit andin assembling any device in which the units are employed, it is not nec essary to furnish any further support for the units than to secure these terminals in such manner as to establish the desired electrical connections.

Referring to Figs. 9 and 10, 1t- Wlll be seen that the series of stationary contacts,

-Conce ntric with the series 30 is arranged a second series of stationary contacts 32. Pivot'ed'a-t 33 is, a movable contact element 34 which, at its ends, carries a contacting device 35 adapted to enga c with the series 30 of stationary. contacts w ile at the other end of the element 34 is a device 36 adapted to "engage with the contacts of the series 32.

Thecontact element 34 is of conducting material, or a conductor may belaid along it so as to electrically connect the devices 35 and 36 so that electrical connection is est-ablijshed along the lever-or arm 34 between the two series of contacts- 30 and 32. Upon the opposite side of the plate 31 are arranged the resistance units as before described, this arrangement being as shown in Fig. 9, from which it will be seen that the resistance units are arranged in concentric circles to c0rrespend with the series of stationary contacts.

.The stationary contacts may be secured in position by means of holts'37 which extend through the plate 31 and project from the rear thereof. The resistance units are then of, that the securing of the unit as described,

not. only mechanically secures but electrically connects the same. As shown in Fig.

- 9, the adjacent terminals of adjacent units in the same circle are connected to the same bolt and therefore a continuous connection is established through the resistive conductors of all the units of the circle and the resistive conductor of each unit is connectedv to three of the stationary contacts, these connections being made at the extremities of the units conductor and at a point intermediate of its end sothat there is in each unit two steps of resistive conductor. Of course, by extending thisarrangement any number of steps might be provided in the unit.

The construction of the contact devices and 36 is shown in details in Figs. 12 and 13. Each of these devices comprises a plurality of skateshoes 38, rectangular in outline and comparatively long I and narrow and with curved ends extending le gthwise across the arm; that is, the shoes extend lengthwise in the direction of movement. Each shoe is pressed against the stationary contacts by a spring 39 at each end. Each spring is partly-inc'losed in a tubular case 40 which has a closed, rounded outer end, which case sits in av considerably large aperture in the shoe. The spring and its case extend into a considerably larger hole drilled in the lower face of the pivoted arm, there being one hole for each spring. A

flexible conductor 41 is secured to each shoe and also to the contact arm, givingdirect electrical connection between these parts. The above construction secures excellent contact between the shoes and resistance contacts, gives uniform pressure and will permit the parts to be readily renewed or replaced. This construction gives a flexible form of skate-contact which rides readily over any unevenness upon the stationary contacts without breaking the circuit or seriously affecting the. contact. It will be seen that the contacts at the ends of the le-' ver arn1 are independently movable and that the armis'balanced upon its pivot, being supported at both ends. It is thus easily turned even thouvh the surface over which the contacts ride is uneven, due to arcing or other causes, not only because of the balancv ing feature, but because the skates are of such construction as to obviate such engagement of stationary and movable contacts hat movement might be nrevented. These considerations are of peculiarjmportance in connection with rheostats which are controlled from a distance.

The connections established by the rheostat are diagrammatically shown in Fig. 11

in which the rheostat is shown as connected to the conductors 42 and 43 in the circuit the current of which is to be controlled. It will be apparent from the position of the contact arm as shown that the circuit will be from the conductor 42, through the resistance 44, connected to the series 30 of stationjment, it may be embodied in other constructions and is not, therefore, limited to the structure shown in the drawings.

Having thus described my invention, I declare that what I claim as new and desire to secure by Letters Patent, is 4 1. The combination with a removable resistance unit comprising a flexible resistive ribbon, metallic terminal contact pieces connected to the two ends of said ribbon respectively, a supporting block of insulating material secured to said terminal contact pieces, of a support for said unit, said contact pieces bein adapted to be removably attached to said support and when so attached to support the unit as a'whole, said ribbon being freely exposed to the air throughout the greater part of its len 2. The combination with a removab e resistance unit comprising a flexible resistive ribbon freely exposed to the air, and metallic terminal contact pieces connected to the two ends of the ribbon respectively, of a common support which said contact pieces are adapted to be attached to or removed from, said terminal contact pieces being adapted when attached to said support to support the unit as 'a whole and to permit the removal of said unit asa whole.-

; 3. A removable resistance unit having greater lengththan breadth so that it is long and narrow, said unit comprislng two terminal contact pieces at the same end of the unit and comprising a ribbon-like resistance connectin said terminal contact pieces, said contact pieces adapted to be attached to a common sup ort and to support the unit as a whole re ative to said common support.

The current will thus a metallic support extending alon a ing 4. A rheostat or heater comprising a plurality of,removable resistance units, each of said unlts comprising a flexible resistlve conductor, a support therefor and a plurality of terminal contact pieces adapted to support the unit as a whole and permit the ready removal of the unit as a whole. 1

5. A removable resistance unit comprising the greatest dimension of said unit, insu ating pieces carried by said support at a distance from each other, terminal contact pieces ada ted to jointly support said unit as a who e, and a metallic resistance ribbon having its ends connected to said terminal contact pieces respectively. I I

6. A rheostat or heater comprising in combination a support and a plurality of individually removable resistance units mounted thereon, each of said units comprising a flexible resistive conductor and means for adjusting the tension upon said conductor.

- 7. A rheostat or heater comprising a -plurality of individually removable resistance units, each of said units comprising a metal element for supporting the parts of the unit, said parts including a plurality of insulate ements, and a flexible, ribbon-like resistive conductor stretched between said sulating elements.

8. A rheostat or heater comprising a plurality of individually removable resistance units, each of said unitscomprising a metallic resistive conductor freely exposed to the air,.a support forthe same comprising insulating elements and ineans for adjusting the distance between said elements.

9. In a rheostat or heater, the combination with a refiexed metallic resistive conductor.

freely exposed to the air, said conductor being in the form of a long narrow arch, and a support for the same. comprising insulating elements and means for adjusting the distance between said elements.

10. In a rheostat or heater, the combination with a refiexed metallic ribbon-like resistive conductor freely exposed to the air, said conductor being in. the form of a long narrow arch, and a support for the same comprising insulating elements and means for adjusting the distance between s'aid elements.

1.1.' In a resistance device, the combination with a metallic su port, of two porcelain elements supported by said metallic support and adapted to act as insulating supports, and a resistive conductor stretched between said porcelain elements and outside of said metallic support.

12. In a rheostat or heater, the combina- 14. In a rheostat or heater, the combination with a suitable support, of contacts thereon, a contact member movable over said contacts to cut out or insert a step of resistance as it moves from one contact to the next, and a plurality of individually removable resistance units each comprising a support and a resistive conductor thereon constituting a plurality of steps, the termmals of the steps being arranged at the same end of the unit.

1-5. In a rheostat or' heater, the combination with a suitable support, of cont-acts thereon, a contact member movable over said contacts to cut out or insert a step of resistance as it moves from one contact to the next, and aplurality of resistance units each comprising a support and a resistive ribbon conductor thereon constituting a plurality of steps, the terminals of the steps be.

ing arranged at the same end of the unit.

16. In a rheostat, the combination with a series of stationary contacts, of a support therefor, a series of resistance steps corresponding to said contacts and comprising flexible resistive conductors arranged in the form of long narrow arches, and means for supporting said arches in a position such that a line parallel to the sides of an arch and passing through the center thereof will be substantially normal to the surface in which the stationary contacts lie.

17. Ina rheostat, the combination with a series of individually removable resistance units each comprising a rlbbon-llke resist ance, of a series of contacts therefor, a second series of lndividually removable resistance units each comprising a ribbon-like re.-'

sistance, a second series of contacts therefor and a resistance-varying movable element adapted to act as a conducting bridge between the two series of resistance steps, and means for moving said movable element to vary the resistance.

18. In a rheostat, the combination with a series of steps of resistance, of a series of contacts therefor, a second series of steps of resistance, a second series of contacts therefor and a resistance-varying movable element adapted to act as a conducting bridge between the two series of resistance steps,

being substantially parallel to the greatest dimension throughout the greatest part of the length of the conductor.

20. A rheostat or heater comprising a plurality of resistance units, each of said units comprising a support, a flexible resistive conductor thereon, and terminals connected to said conductor at one end of the unit, said terminals being adapted to jointly support the unit as a Whole.

21. In a rheostat or heater, the combination with a plurality of contacts, of an insulating support therefor, a movable contactelement adapted to move over said contacts and a plurality of resistance units connected to said contacts, each of said units comprising a support and a flexible resistive conduct-or thereon, and each of said units being supported with its greatest dimension substantially at right angles to the plane of said support.

A resistance unit having a metallic ribbon so arranged as to have two sections of the ribbon substantially parallel to each other and a support for said ribbon, said support being between the said sections and the greatest dimension of said support being substantially parallel to the said sections of said ribbon. 2 0

In testimony whereof I aflix my signature. in presence of two witnesses.

H. \VARD LEONARD. \Vitnesses:

J. S. Woosrrn,

GEO. N. Kara. 

